Abstract Proline-catalysed reactions between α-branched aldehydes and sulfonyl azides provide scalemic configurationally stabilised α-sulfamidated products with ee values of up to 86%. The reactions can also be carried out in a one-pot fashion, with catalyst, aldehyde, sulfonyl chloride and sodium azide. The proposed mechanism differs fundamentally from the mechanistic model usually ascribed to enamine catalysis, containing as a key step the ...